Re: [PATCH] dmaengine: xilinx_dma: Add missing check for empty list

From: Vinod Koul <vkoul@kernel.org>
To: Sebastian von Ohr <vonohr@smaract.com>,
	Appana Durga Kedareswara rao <appana.durga.rao@xilinx.com>,
	Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>,
	Michal Simek <michal.simek@xilinx.com>
Cc: dmaengine@vger.kernel.org
Subject: Re: [PATCH] dmaengine: xilinx_dma: Add missing check for empty list
Date: Fri, 6 Mar 2020 19:04:27 +0530	[thread overview]
Message-ID: <20200306133427.GG4148@vkoul-mobl> (raw)
In-Reply-To: <20200303130518.333-1-vonohr@smaract.com>

On 03-03-20, 14:05, Sebastian von Ohr wrote:
> The DMA transfer might finish just after checking the state with
> dma_cookie_status, but before the lock is acquired. Not checking
> for an empty list in xilinx_dma_tx_status may result in reading
> random data or data corruption when desc is written to. This can
> be reliably triggered by using dma_sync_wait to wait for DMA
> completion.

Appana, Radhey can you please test this..?

> 
> Signed-off-by: Sebastian von Ohr <vonohr@smaract.com>
> ---
>  drivers/dma/xilinx/xilinx_dma.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index a9c5d5cc9f2b..5d5f1d0ce16c 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -1229,16 +1229,16 @@ static enum dma_status xilinx_dma_tx_status(struct dma_chan *dchan,
>  		return ret;
>  
>  	spin_lock_irqsave(&chan->lock, flags);
> -
> -	desc = list_last_entry(&chan->active_list,
> -			       struct xilinx_dma_tx_descriptor, node);
> -	/*
> -	 * VDMA and simple mode do not support residue reporting, so the
> -	 * residue field will always be 0.
> -	 */
> -	if (chan->has_sg && chan->xdev->dma_config->dmatype != XDMA_TYPE_VDMA)
> -		residue = xilinx_dma_get_residue(chan, desc);
> -
> +	if (!list_empty(&chan->active_list)) {
> +		desc = list_last_entry(&chan->active_list,
> +				       struct xilinx_dma_tx_descriptor, node);
> +		/*
> +		 * VDMA and simple mode do not support residue reporting, so the
> +		 * residue field will always be 0.
> +		 */
> +		if (chan->has_sg && chan->xdev->dma_config->dmatype != XDMA_TYPE_VDMA)
> +			residue = xilinx_dma_get_residue(chan, desc);
> +	}
>  	spin_unlock_irqrestore(&chan->lock, flags);
>  
>  	dma_set_residue(txstate, residue);
> -- 
> 2.17.1

-- 
~Vinod